Physicists at Imperial College London are developing a new challenge to the DVD – an optical disk that will be able to store up to one Terabyte (1,000 Gigabytes) of data.

The new disks, dubbed MODS – Multiplexed Optical Data Storage – would be double sided and dual layer, and seek to challenge DVDs’ domination of the audiovisual optical disk market.

The developers estimate that it would be possible to store up to 472 hours of film, on one optical disk the size of a CD or DVD. They also anticipate that MODS disks would cost approximately the same to manufacture as an ordinary DVD and that any system playing them would be backwards compatible with existing optical formats.

Team leader Dr Török believes that the first disks could be on the shelves between 2010 and 2015, as long as his team are able to secure funding for further development.

The MODS disks will not be the first to challenge DVDs’ domination of the audiovisual optical disk market. BluRay disks, which boast five times the capacity of a DVD at 25GB per layer, are likely to be released towards the end of 2005 for the home market.

Leader of the research team Dr Török emphasises the higher capacity of the MODS discs: "We estimate that we will be able to store about one Terabyte per disk using our new method. This translates to about 250GB per layer, 10 times the amount that a BluRay disk can hold.”

The science bit

Imperial are attending the Asia-Pacific Data Storage Conference 2004 in Taiwan to explain how the new discs will work.

Under magnification the surface of CDs and DVDs appear as tiny grooves filled with pits and land regions. These pits and land regions represent information encoded into a digital format as a series of ones and noughts. When read back, CDs and DVDs carry one bit per pit, but the Imperial researchers have come up with a way to encode and retrieve up to ten times the amount of information from one pit.

"Unlike existing optical disks, MODS disks have asymmetric pits, each containing a ‘step’ sunk within at one of 332 different angles, which encode the information," they explain. The Imperial researchers have developed a method that can be used to make a precise measurement of the pit orientation that reflects the light back. A different physical phenomenon is used to achieve the additional gain.

“We came up with the idea for this disk some years ago,” says Dr Török. “But did not have the means to prove whether it worked. To do that we developed a precise method for calculating the properties of reflected light, partly due to the contribution of Peter Munro, a PhD student working with me on this project.

"We are using a mixture of numerical and analytical techniques that allow us to treat the scattering of light from the disk surface rigorously rather than just having to approximate it.”